New Deck FAQ

What is pressure-treated wood?

Over 70 years ago, Dr. Karl Wolman invented the process of infusing preservative deeply into wood products. Today, a giant industry has grown up around his quest to invent a wood that can last forever.

Pressure treating is a process that forces a chemical preservative deep into the wood. The wood product is placed into a humongous cylindrical holding tank, and the tank is depressurized to remove all air. The tank is then filled with the preservative under high pressure, forcing it deeply into the wood. The tank is then drained and the remaining preservative reused. The wood is removed from the tank and prepared for shipment to your local lumberyard.

Needless to say, this process makes the wood quite unappetizing to all vermin, insects, and fungus, which accounts for its 20 year plus lifespan under the harshest conditions!

What is the chemical preservative used, and is it dangerous?

Until 2003, the preservative most commonly used in residential pressure-treated lumber was chromated copper arsenate (CCA), an extremely toxic chemical. CCA is so toxic that the Environmental Protection Agency, over 20 years ago, imposed strict guidelines regarding the manufacturing practices of companies using CCA.

Your local home store or lumberyard is now selling lumber treated with less toxic alternatives... amine copper quat (ACQ) and copper azone (CA)... though you may find other chemical combinations in specific areas.

If CCA is potentially dangerous, should I tear out my old deck? It's otherwise in great shape.

By replacing your existing deck you can avoid the potential risk associated with CCA treated lumber.

Why does pressure-treated wood need to be coated with a preservative? If it's so dang tough, why bother?

Though the infused preservative prevents rot, it does not inhibit weathering...
The effects of the elements on pressure-treated wood are no different than with ordinary wood. So a preservative is a must, and should be applied as soon as possible after your project is completed.

Rapid drying causes warping, cracking and splintering...
Pressure-treated lumber is shipped to the lumberyard in stacks that are tightly bundled and damp... sometimes even wet. If you go and pick through a bin of pressure-treated lumber, you will see some pieces are straight, and others moderately to wildly warped. The warped pieces are invariably the pieces that were on the outside of the bundle... exposed to the sun and air and dried on one side. Once the bundle is broken they twist like Chubby Checker!

Once installed in your project and subjected to freely moving air and the sun, the same effect occurs. Shrinkage of deck boards can be excessive, in both length and width, and twisting can loosen railings and floor boards. Railings can become cracked and splintery, making them uncomfortable to use.

Applying a preservative slows drying, so less shrinkage occurs and the surface of the wood remains smoother longer. The preservative should be applied immediately upon completion of the project. Be sure that the preservative you purchase is recommended for use with pressure-treated wood. More about this in the next section...

Can pressure-treated wood be painted or stained? Definitely!

Tips for working with pressure-treated wood...

• Always install pressure-treated deck flooring with the bark side up.
  Pressure-treated wood tends to cup as it dries. Cupping is the tendency wood to bend along its width away from the bark side. You can tell which side in the bark side by looking at the end grain of the board.
• Predrill any nail or screw holes within an inch of the end of the board. This lessens the chance of splitting the board while fastening it. Even if it doesn't split when you initially fasten it down without predrilling, it will very likely do so later as the wood dries out.
• Use the right fasteners.
  Use only screws or nails that are galvanized and designed for pressure-treated wood. Any of the many styles of galvanized metal brackets and reinforcements commonly used in construction today can be used outside with pressure-treated wood.
• Do not allow any space between boards when laying in a deck floor.
  Putting spacers between floor boards is the amateur's biggest mistake. pressure-treated wood shrinks, even if you coat it with a preservative! Years ago when it first came on the market, people installed deck floors like good old untreated Douglas Fir, installing the boards with spacers between them. Wood shrinkage typically caused 3/4" or wider gaps in the floor... just the right width to snap off a high heel!
• Can deck posts be buried?
  Pressure-treated wood will not rot, even if buried, making it ideal for fence, mailbox, and light posts. Check with your local building inspector to see if code allows burial of pressure-treated deck posts in your area, or if the concrete footing must be exposed above ground level.

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